Gas oil composition and method for producing the same

ABSTRACT

A gas oil composition comprising at least 20.0% by volume total aromatic content, at least 1.0% by volume bicyclic aromatic content, at least 0.2% by volume trior higher cyclic aromatic content, no more than 18.0% by mass naphthenobenzenes, and no more than 10 ppm by mass sulfur content, and having a density (15° C.) of at least 0.8200 g/cm3, and an ASTM colour of at least 0.2, characterised in that the gas oil composition is obtained by hydrogenation-desulfurisation of the stock oil described below, which contains cracked gas oil fraction: stock oil comprising at least 25.0% by volume total aromatic content, at least 15.0% by mass total naphthene content, at least 4.0% by mass bicyclic naphthene content, at least 1.0% by mass tricyclic naphthene content, and at least 0.50% by mass sulfur content, and having a 90% distillation temperature of at least 340.0° C. The gas oil composition of the present invention has excellent oxidative stability.

FIELD OF THE INVENTION

The present invention relates to a gas oil composition used in diesel engines and the like, and to a method for producing the same.

BACKGROUND OF THE INVENTION

Generally, there tends to be greater demand for the petroleum products referred to as white oils, e.g. gasoline, gas oil and kerosene, than for the heavy oils that comprise heavy fuel oil components, and this trend has become more marked since, for example, the recent conversion from heavy oil to natural gas for industry. Petroleum products are referred to as complementary products, and because heavy oil components are also generated in the process by which white oils are produced, usually, in order to increase the amount of white oils produced, the heavy fuel oil components are cracked and used as white oil base material (a treatment referred to as an upgrading process). However, the white oil base material obtained by cracking heavy fuel oil components is of limited use as a product because it does not meet the necessary regulations, and even if it did meet the necessary regulations, its performance in practice would be problematical. There is a problem with oxidative stability when cracked gas oil fraction obtained from a heavy fuel oil cracking unit is used as base material for gas oil.

Oxidative stability is an important property of gas oil, as it affects its usage status and its performance in practice. Many means have been suggested for improving the oxidative stability of gas oil. Gas oil with improved oxidative stability, which contains in its base material desulfurised gas oil obtained by desulfurising cracked gas oil fraction, has also been disclosed.

For example, Japanese unexamined patent application 2008-144156 discloses a gas oil composition having oxidative stability that has been improved mainly by limiting its styrene compounds content and diene compounds content to within specified ranges; this gas oil composition contains, as base material, desulfurised gas oil obtained by desulfurising cracked gas oil fraction.

Japanese unexamined patent application 2013-203752 discloses a gas oil composition having oxidative stability that has been improved mainly by limiting its benzanthracenes content to within a specified range; this gas oil composition contains, as base material, desulfurised gas oil obtained by desulfurising cracked gas oil fraction.

However, as described above, cracked gas oil fraction is problematical in terms of oxidative stability when used as a base material for gas oil. Moreover, diesel cars are subject to stricter exhaust gas regulations, the injection pressure inside the engine combustion cylinder is increasing year on year, and the fuel in the fuel injection pump and injector is at ever higher pressure and temperature, and so there is even greater demand for the provision of a gas oil composition with excellent oxidative stability. Therefore, the aim of the present invention is to provide a gas oil composition of excellent oxidative stability using cracked gas oil fraction as the stock oil, and to provide a method for producing the same.

According to the present invention there is provided a gas oil composition comprising at least 20.0% by volume total aromatic content, at least 1.0% by volume bicyclic aromatic content, at least 0.2% by volume tri- or higher cyclic aromatic content, no more than 18.0% by mass naphthenobenzenes, and no more than 10 ppm by mass sulfur content, and having a density (15° C.) of at least 0.8200 g/cm³, and an ASTM colour of at least 0.2, characterised in that the gas oil composition is obtained by hydrogenation-desulfurisation of the stock oil described below, which contains cracked gas oil fraction: stock oil comprising at least 25.0% by volume total aromatic content, at least 15.0% by mass total naphthene content, at least 4.0% by mass bicyclic naphthene content, at least 1.0% by mass tricyclic naphthene content, and at least 0.50% by mass sulfur content, and having a 90% distillation temperature of at least 340.0° C.

According to the present invention there is also provided a method for producing gas oil composition comprising at least 20.0% by volume total aromatic content, at least 1.0% by volume bicyclic aromatic content, at least 0.2% by volume tri- or higher cyclic aromatic content, no more than 18.0% by mass naphthenobenzenes, and no more than 10 ppm by mass sulfur content, and having a density (15° C.) of at least 0.8200 g/cm³, and an ASTM colour of at least 0.2, characterised in that the method for producing gas oil composition comprises hydrogenation-desulfurisation of the stock oil described below, which contains cracked gas oil fraction: stock oil comprising at least 25.0% by volume total aromatic content, at least 15.0% by mass total naphthene content, at least 4.0% by mass bicyclic naphthene content, at least 1.0% by mass tricyclic naphthene content, and at least 0.50% by mass sulfur content, and having a 90% distillation temperature of at least 340.0° C.

The present invention can provide a gas oil composition of excellent oxidative stability where cracked gas oil fraction is used as the stock oil, and a method for producing the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram showing the relationship between the desulfurisation unit outlet temperature and the polycyclic aromatics content and sulfur content of the desulfurised gas oil.

DETAILED DESCRIPTION OF THE INVENTION

The stock oil used in the present invention has a total aromatic content of at least 25.0% by volume, preferably from 25.0 to 35.0% by volume, and more preferably from 25.0 to 30.0% by volume. If the aromatic content is lower, the reaction may be insufficiently exothermic, and the post-desulfurisation oxidative stability may be insufficient; if it is too high, the post-desulfurisation cetane index will be lower, which may result in disadvantages such as ignition failure at low temperature. The aromatic content can, for example, comprise from 16.0 to 22.0% by volume monocyclic aromatics, from 5.0 to 10.0% by volume bicyclic aromatics and from 1.0 to 4.0% by volume tri- and higher cyclic aromatics.

The total naphthene content in the stock oil is at least 15.0% by mass, preferably from 15.0 to 25.0% by mass, more preferably from 17.0 to 25.0% by mass, and yet more preferably from 21.0 to 25.0% by mass. The monocyclic naphthene content is, for example, from 10.0 to 17.0% by mass. The bicyclic naphthene content is at least 4.0% by mass, preferably from 5.0 to 7.0% by mass. The tricyclic content is at least 1.0% by mass, preferably from 1.5 to 2.5% by mass. If the naphthene content is lower, the post-desulfurisation oxidative stability of the gas oil may deteriorate; if it is too high, the post-desulfurisation cetane index will decrease, which may result in ignition failure at low temperature, for example.

The sulfur content in the stock oil is at least 0.50% by mass, preferably from 0.50 to 1.60% by mass, more preferably from 0.80 to 1.50% by mass, and yet more preferably from 1.00 to 1.50% by mass. The higher the sulfur content, the more readily the exothermic reaction occurs, and the easier it is to obtain gas oil having the desired oxidative stability; however, if the sulfur content is too high, the life of the catalyst may decrease, and there is a risk of desulfurisation unit failure due for example to its effect on the materials of the reactor, pipes, etc.

The stock oil 10% distillation temperature is, for example, from 210.0 to 270.0° C., and the 50% distillation temperature is, for example, from 280.0 to 310.0° C. The 90% distillation temperature is at least 340.0° C., preferably from 340.0 to 380.0° C., more preferably from 340.0 to 370.0° C., and yet more preferably from 350.0 to 370.0° C. The higher the 90% distillation temperature, the higher the reaction temperature required to achieve the desired 10 ppm by mass sulfur content, and the easier it is to obtain gas oil of good oxidative stability; however, if it is too high, the amount of wax in the stock oil increases and it becomes difficult to achieve the desired pour point and plugging point.

The density (15° C.) of the stock oil can be, for example, from 0.8400 to 0.8600 g/cm³. The kinematic viscosity can be, for example, from 4.0 to 6.0 mm²/s; the pour point can be, for example, no higher than +2.5° C.; and the plugging point can be, for example, no higher than +5° C.

The stock oil used in the present invention can be prepared by mixing cracked gas oil fraction with another gas oil base material (hereafter, stock oil base material).

The cracked gas oil fraction is a gas oil fraction or the like distilled from a heavy oil upgrading process: examples include directly desulfurised gas oil (hereafter referred to as RGO) obtained from a direct desulfurisation unit; indirectly desulfurised gas oil obtained from an indirect desulfurisation unit; light cycle oil (hereafter referred to as LCO) obtained from a fluid catalytic cracking unit; and thermally cracked gas oil obtained from a thermal cracking unit. In view of the oxidative stability of the gas oil after desulfurisation, the cracked gas oil fraction is preferably an RGO.

The total aromatic content in the RGO is preferably at least 25.0% by volume, more preferably from 25.0 to 40.0% by volume, and yet more preferably from 30.0 to 40.0% by volume. If the total aromatic content is lower, the exothermic reaction may not proceed readily, and the oxidative stability of the post-desulfurisation gas oil may deteriorate; if it is higher, the cetane index of the post-desulfurisation gas oil will decrease, which may result in disadvantages such as ignition failure at low temperature. For example, the monocyclic aromatic content can be from 20.0 to 35.0% by volume, the bicyclic aromatic content can be from 2.5 to 4.5% by volume, and the tri- and higher cyclic aromatic content can be from 1.0 to 2.0% by volume. Preferably, the total naphthene content is at least 15.0% by mass, the bicyclic naphthene content is at least 4.0% by mass, and the tricyclic naphthene content is at least 1.0% by mass. The monocyclic naphthene content can, for example, be from 14.0 to 20.0% by mass. If the naphthene content is lower, the oxidative stability may deteriorate; if it is higher, the cetane index will decrease, which may result in disadvantages such as ignition failure at low temperature. The sulfur content is preferably at least 0.01% by mass.

The RGO can for example have a 10% distillation temperature of from 210.0 to 240.0° C., and a 50% distillation temperature of from 280.0 to 320.0° C. Its 90% distillation temperature is preferably no higher than 380° C., more preferably no higher than 370° C. If its 90% distillation temperature is too high, the amount of wax increases and filter-plugging may occur at low temperature. The density (15° C.) is preferably no higher than 0.8700 g/cm³. Too high a density may increase the amount of particulate matter in the exhaust gas. The kinematic viscosity can be from 3.0 to 7.0 mm²/s, the pour point can be no higher than 2.5° C., and the plugging point can be no higher than +5° C., for example.

The LCO total aromatic content is preferably at least 60.0% by volume, more preferably from 65 to 80% by volume, and yet more preferably from 70 to 80% by volume. If the total aromatic content is lower, there is less of an exothermic reaction, and the post-desulfurisation oxidation stability may deteriorate; if it is higher, the post-desulfurisation cetane index will decrease, which may result in ignition failure. For example, the monocyclic aromatic content can be from 15.0 to 30.0% by volume, the bicyclic aromatic content can be from 20.0 to 40.0% by volume, and the tri- and higher cyclic aromatic content can be from 5.0 to 20.0% by volume. Preferably, the total naphthene content is at least 15.0% by mass, the bicyclic naphthene content is at least 3.0% by mass, and the tricyclic naphthene content is at least 1.0% by mass. The monocyclic naphthene content can, for example, be from 12.0 to 17.0% by mass. If the naphthene content is lower, the post-desulfurisation oxidative stability may be insufficient; if it is higher, the cetane index will decrease, which may result in disadvantages such as ignition failure. The sulfur content is preferably at least 0.07% by mass.

The LCO can for example have a 10% distillation temperature of from 210.0 to 230.0° C., and a 50% distillation temperature of from 250.0 to 280.0° C. Its 90% distillation temperature is preferably no higher than 370.0° C. If its 90% distillation temperature is too high, the amount of wax increases, which may result in disadvantages such as filter-plugging in cold weather. The density (15° C.) is preferably no higher than 0.9800 g/cm³, more preferably from 0.9200 to 0.9500 g/cm². If the density is too low, the post-desulfurisation oxidative stability may decrease; if it is too high, the cetane index will decrease, which may result in ignition failure. The kinematic viscosity can be from 2.0 to 4.0 mm²/s, the pour point can be from −15 to −35° C., and the plugging point can be no higher than −5 to −20° C., for example.

The cracked gas oil fraction is preferably from 1 to 35% by volume, more preferably from 5 to 30% by volume, of the stock oil. If there is too much cracked gas oil fraction, the cetane index of the product may decrease; if there is too little, the reaction tower outlet temperature will decrease and it may not be possible to obtain gas oil composition having the desired oxidative stability. When the cracked gas oil fraction is RGO, said RGO is preferably from 5 to 30% by volume, more preferably from 15 to 30% by volume, and yet more preferably from 25 to 30% by volume, of the stock oil. If there is too much RGO, the cetane index of the product may decrease; if there is too little, it may not be possible to obtain gas oil composition having the desired oxidative stability. When the cracked gas oil fraction is LCO, said LCO is preferably from 1 to 10% by volume, more preferably from 5 to 10% by volume, of the stock oil. If there is too much LCO, the cetane index of the product may decrease; if there is too little, the reaction tower outlet temperature will decrease and it may not be possible to obtain gas oil composition having the desired oxidative stability.

The stock oil base material can be a gas oil fraction obtained from an atmospheric pressure distillation unit (hereafter, direct distillation gas oil).

In the present invention, gas oil composition is obtained by hydrogenation-desulfurisation of the stock oil described above. The resulting gas oil composition has a total aromatic content of at least 20.0% by volume, preferably from 21.0 to 25.0% by volume. The monocyclic aromatic content is, for example, from 18.0 to 22.0% by volume. The bicyclic aromatic content is at least 1.0% by volume, preferably from 2.0 to 3.0% by volume. The tri- and higher cyclic aromatic content is at least 0.2% by volume, preferably from 0.5 to 1.2% by volume. If the aromatic content is lower, the seal material of the fuel injection system may contract and cause fuel bleeding; if it is higher, there may be more black smoke in the exhaust gas.

The resulting gas oil composition contains naphthenobenzenes at no more than 18.0% by mass, preferably from 13.0 to 16.5% by mass, more preferably from 13.0 to 15.0% by mass. If the naphthenobenzene content is lower, the seal material of the fuel injection system may contract and cause fuel to bleed; if it is higher, the oxidative stability may deteriorate. The monocyclic naphthenobenzene content is preferably no more than 15.0% by mass, more preferably from 9.0 to 13.0% by mass, yet more preferably from 9.0 to 12.0% by mass, and particularly preferably from 9.0 to 11.0% by mass. If the monocyclic naphthenobenzene content is lower, the seal material of the fuel injection system may contract and cause fuel to bleed; if it is higher, the oxidative stability may deteriorate. The bicyclic naphthenobenzene content is preferably no more than 5.0% by mass, more preferably from 1.0 to 4.0% by mass, and yet more preferably from 1.0 to 3.0% by mass. If the bicyclic naphthenobenzene content is too high, the oxidative stability tends to deteriorate, which is undesirable. The sulfur content is no higher than 10 ppm by mass.

In the present invention, “monocyclic naphthenobenzenes” includes naphthenobenzenes and alkyl group-bearing naphthenobenzenes; examples include indane and tetralin. “Bicyclic naphthenobenzenes” includes bicyclic naphthenobenzenes and alkyl group-bearing bicyclic naphthenobenzenes; examples include octahydroanthracene and alkyloctahydroanthracenes. “Naphthenobenzenes” includes monocyclic naphthenobenzenes, bicyclic naphthenobenzenes, and polycyclic naphthenobenzenes.

The ASTM colour is at least 0.2, preferably at least 0.5, more preferably from 1.0 to 2.0. If the ASTM colour is too low the oxidative stability deteriorates, and if it is too high there is an increase in the amount of black smoke in the exhaust gas; these situations are undesirable. The density (15° C.) is at least 0.8200 g/cm², preferably from 0.8200 to 0.8600 g/cm². The 10% distillation temperature can be, for example, from 220.0 to 250.0° C., the 50% distillation temperature can be, for example, from 270.0 to 300.0° C., and the 90% distillation temperature can be, for example, from 330.0 to 360.0° C. The kinematic viscosity is from 2.5 to 5.5 mm²/s, the pour point is no higher than 2.5° C., the plugging point is no higher than +1° C., the cetane index is preferably from 45 to 60, more preferably from 50 to 60, and yet more preferably from 55 to 58. If the cetane index is too high, there may be an increase in unburned hydrocarbons in the exhaust gas; too low a cetane index may result in start-up failure.

The inventive gas oil composition has excellent oxidative stability. For example, if oxidative stability can be reflected by induction time in the PetroOXY method, in the inventive gas oil composition it is preferably at least 70 minutes, more preferably at least 90 minutes, yet more preferably at least 125 minutes, and particularly preferably at least 140 minutes.

The abovementioned gas oil composition with excellent oxidative stability is obtained by hydrogenation-desulfurisation using the stock oil described above. Gas oil composition of particularly excellent oxidative stability is obtained by appropriately controlling the reaction temperature in the desulfurisation unit reactor, and the sulfur content and aromatic content in the stock oil. The hydrogenation-desulfurisation is performed under conditions that will yield the gas oil composition described above. For example, the hydrogenation-desulfurisation can be performed as follows.

The hydrogenation-desulfurisation can be performed using a desulfurisation unit in which a known catalyst such as a cobalt-molybdenum catalyst or nickel-molybdenum catalyst is used. The desulfurisation conditions should be adjusted appropriately to yield desulfurised gas oil having a sulfur content of no greater than 10 ppm by mass; the unit outlet temperature must be in a region in which polycyclic naphthene dehydrogenation is dominant.

Inside the desulfurisation unit reactor, dearomatisation occurs at the same time as the desulfurisation, and the amount of polycyclic aromatics having two or more rings will decrease as dearomatisation proceeds. Because desulfurisation and dearomatisation are exothermic reactions, the desulfurisation reaction tower outlet temperature will become higher than the inlet temperature. Consequently, there is a boundary temperature at which, if naphthene dehydrogenation is dominant, the polycyclic aromatic content will tend to increase as the temperature increases.

Specifically, if the unit outlet temperature is no higher than a prescribed value (temperature T0 in FIG. 1) (in the area to the left of temperature T0 in FIG. 1), the dehydrogenation of polycyclic aromatics will be dominant in the unit. Consequently, as the temperature increases and the reaction proceeds, the polycyclic aromatic content will decrease. However, if the unit outlet temperature is higher than the prescribed value T0, the dehydrogenation of polycyclic aromatics having two or more rings will be dominant in the unit, and so as the temperature increases and the reaction proceeds, the polycyclic aromatic content in the desulfurised oil will increase.

It should be noted that the graph in FIG. 1 illustrates the polycyclic aromatic content and the sulfur content for ease of understanding, and is not accurate.

The oxidative stability can be improved by adjusting the unit outlet temperature to within a region in which polycyclic naphthene dehydrogenation is dominant inside the unit, and having a suitable amount of naphthenes in the stock oil, to increase the polycyclic aromatic content and decrease the naphthenobenzene content in the desulfurised gas oil. The oxidative stability can be increased particularly if the stock oil that will be hydrogenated-desulfurised has the specific properties described above.

The unit outlet temperature can be kept within the desired range by adjusting the liquid-space velocity, reaction tower outlet hydrogen partial pressure, and hydrogen-oil ratio as appropriate, depending on the type of catalyst used in the unit, and by adopting a suitable reaction tower outlet temperature. For example, if a commercial CoMo or NiMo desulfurisation catalyst is used as the catalyst, the liquid-space velocity can be from 0.4 to 1.5 h⁻¹, the reaction tower outlet hydrogen partial pressure can be from 3.5 to 6.2 MPa, and the hydrogen-oil ratio can be from 100 to 300 NL/L.

The region (temperature) in which polycyclic naphthene dehydrogenation is dominant can be determined, for example, as follows. If the reaction temperature is increased in order to lower the sulfur content, the two-or-more-ring polycyclic aromatic content also decreases, but there is a boundary point temperature at which the polycyclic aromatic content will increase. The temperature (T0) at which the polycyclic aromatic content is at its lowest will differ depending on the general desulfurisation unit and operating conditions, and on the properties of the stock oil—for example, depending on the hydrogen partial pressure, catalytic activity, and hydrogen-oil ratio; this temperature can be determined by measuring (e.g. by the JPI method) the aromatics in the gas oil composition obtained, and by measuring the polycyclic aromatic content and the reaction tower outlet temperature. The region (temperature) in which polycyclic naphthene dehydrogenation is dominant is preferably chosen from the region T0° C.−T0+40° C., and is more preferably chosen from the region T0° C.−T0+20° C. An optional region within this region, that is, the upper and lower limits, can be decided to define the region (temperature) in which polycyclic naphthene dehydrogenation is dominant. If the region (temperature) in which it is dominant is too cool, the desired oxidative stability will be difficult to achieve, whereas if it is too hot, the polycyclic aromatic content will increase and the exhaust gas properties may deteriorate.

In the present invention, the gas oil composition can be a manufactured product gas oil, or it can be a base material that is a constituent of manufactured product gas oil. Therefore, the inventive gas oil composition can be used without further modification as a manufactured product, and it can be used as a base material.

Additives can be admixed in when the inventive gas oil composition is used without further modification as a manufactured product, and when it is used as a base material. When it is used as a base material, it can be admixed, for example, with one or more types of kerosene base material, or with one or more types of gas oil base material.

Examples of kerosene base material that can be used include kerosene fraction obtained by atmospheric pressure distillation of crude oil, and desulfurised kerosene obtained by desulfurising said kerosene fraction. It is also possible to use kerosene base material of sulfur content no higher than 10 ppm by mass, obtained by admixing kerosene fraction obtained by atmospheric pressure distillation, and cracked kerosene, in appropriate proportions, and desulfurising the resulting mixture. The cracked kerosene should be a kerosene fraction distilled from an upgrading of a heavy oil such as kerosene fraction obtained from a fluid catalytic cracking unit, or kerosene fraction obtained from a thermal cracking unit; the blend ratio is preferably as high as possible, in accordance with recent societal demands.

Further examples of gas oil base materials include GTL gas oil, which is a paraffin compound manufactured from carbon monoxide and water using the Fischer-Tropsch reaction.

Examples of additives used include antioxidants, lubricity improvers and cold-flow improvers. Commercial antioxidants can be used. Commercial lubricity improvers can be used, such as acid-based lubricity improvers in which the main component is fatty acid, and ester-based lubricity improvers in which the main component is a mono-fatty acid ester of glycerol. These compounds can be used singly, or a combination of two or more can be used. The fatty acid used in the lubricity improver is preferably an unsaturated fatty acid having from 12 to 22 carbons, preferably about 18 carbons, specifically, having a mixture of oleic acid, linoleic acid, linolenic acid, etc. as main component. Examples of the cold-flow improvers used include ethylene-vinyl acetate copolymer, ethylene-alkyl acrylate copolymers, alkenyl succinic acid amides, chlorinated polyethylene, polyalkyl acrylates, and other commercial cold-flow improvers.

EXAMPLES Stock Oil Preparation

RGO and LCO were used as the cracked gas oil fraction; and gas oil fraction 1 (LGO 1) and gas oil fraction 2 (LGO 2), which differed in properties such as type of crude oil and sulfur content, were used as the stock oil base material to be mixed with said gas oil fraction. The respective properties are shown in Table 1. RGO, LCO, LGO 1 and LGO 2 were mixed in the proportions by volume shown in Table 2, to obtain stock oils 1-4. The properties of stock oils 1-4 are shown in Table 2. All properties, etc. were found as described below.

Composition:

Aromatic content: The 1-ring aromatic content, 2-ring aromatic content and 3-or-more-ring aromatic hydrocarbon content were measured in accordance with JPI-5S-49-97 “Petroleum products—Determination of hydrocarbon type—High performance liquid chromatography”. The total of these was deemed the total aromatic content.

Naphthene content, naphthenobenzenes: FI-MS measurements were performed using a JMS-T100GC time-of-flight mass spectrometer (manufactured by JEOL) connected to an HP-6890N gas chromatograph (manufactured by Agilent Technologies); the measured data was corrected using an ion intensity (%) and concentration (% by mass) correction graph obtained using a normal paraffin standard sample, and then, taking the intensity of the whole as 100% by mass, each mass ratio (%) was found. The analysis conditions were as follows:

GC column: FS, deactivated (0.250 mm×5 m, Agilent Technologies)

Column temperature conditions: 300° C. (7 min)

Sample vaporising chamber conditions: 300° C. fixed

MS detector: 300° C.

Sulfur content: Measured in accordance with JIS K 2541-4 “Crude oil and petroleum products—Determination of sulfur content Part 4: Energy-dispersive X-ray fluorescence method”.

Density (at 15° C.): Measured in accordance with JIS K 2249 “Crude oil and petroleum products—Determination of density, and density/mass/volume conversion tables”.

Distillation characteristics: Measured in accordance with JIS K 2254 “Petroleum products—Determination of distillation characteristics”.

Kinematic viscosity (at 30° C.): Measured in accordance with JIS K 2283 “Crude oil and petroleum products—Determination of kinematic viscosity and method for calculating viscosity index”.

Pour point: Measured in accordance with JIS K 2269 “Determination of pour point and cloud point of crude oil and petroleum products”.

Plugging point: Measured in accordance with JIS K 2288 “Petroleum products—Gas oil—Determination of plugging point”.

ASTM colour: Measured in accordance with the stimulus value conversion method JIS K 2580 “Petroleum products—Determination of colour”. Measured to one decimal place using simultaneous colour and turbidity meter COH400 (manufactured by Nippon Denshoku Co., Ltd).

Cetane index: Measured in accordance with JIS K 2280-5 “Petroleum products—Determination of octane number, cetane number and calculation of cetane index—Part 5: Cetane index”.

Induction time by the PetroOXY method (induction time): The initial oxygen pressure was set at 700 kPa, and the time taken for the pressure to decrease by 10% from the maximum was measured, as an indicator of oxidative stability, using a PetroOXY oxidative stability testing unit (manufactured by Petrotest). In this test, the test temperature was 140° C., in order to evaluate the oxidative stability at high temperature.

TABLE 1 Unit LGO 1 LGO 2 RGO LCO Monocyclic mass 9.1 14.4 16.8 14.6 naphthene % content Bicyclic mass 3.8 4.8 8.9 4.0 naphthene % content Tricyclic mass 1.3 1.4 3.7 1.3 naphthene % content Total mass 14.2 20.6 29.4 19.9 naphthene % content Monocyclic vol % 14.6 16.9 28.9 24.8 aromatic content Bicyclic vol % 6.9 6.7 3.8 37.2 aromatic content Tri- and vol % 2.9 1.8 1.5 11.5 higher cyclic aromatic content Total vol % 24.4 25.4 34.2 73.5 aromatic content Density g/cm³ 0.8477 0.8523 0.8601 0.9287 Sulfur mass 0.92 1.44 0.02 0.33 content % T10 ° C. 259.5 257.5 231.0 222.0 T50 ° C. 300.0 302.0 303.0 267.5 T90 ° C. 354.5 352.5 367.0 334.0 Kinematic mm²/s 5.3 5.6 5.4 3.2 viscosity (at 30° C.) Pour point ° C. 0 −2.5 2.5 −32.5 Plugging ° C. 1 −1 3 −12 point

TABLE 2 Stock Stock Stock Stock Unit oil 1 oil 2 oil 3 oil 4 LGO 1  74%  0%  0%  93% LGO 2  0%  80%  93%  0% RGO  26%  20%  0%  0% LCO  0%  0%  7%  7% Total 100% 100% 100% 100% Monocyclic mass % 11.1 15.7 14.1 9.4 naphthene content Bicyclic mass % 5.1 5.7 4.6 3.8 naphthene content Tricyclic mass % 1.9 1.8 1.3 1.3 naphthene content Total mass % 18.1 23.3 20.0 14.6 naphthene content Monocyclic vol % 18.3 19.9 17.6 15.3 aromatic content Bicyclic vol % 6.1 5.9 8.8 9.0 aromatic content Tri- and vol % 2.5 1.7 2.3 3.5 higher cyclic aromatic content Total vol % 26.9 27.5 28.8 27.8 aromatic content Density g/cm³ 0.8508 0.8537 0.8576 0.8535 Sulfur mass % 0.69 1.13 1.36 0.88 content T10 ° C. 253.0 251.5 257.0 255.5 T50 ° C. 301.0 302.0 300.5 298.0 190 ° C. 356.0 353.5 350.0 351.0 Kinematic mm²/s 5.3 5.4 5.3 5.1 viscosity (at 30° C.) Pour point ° C. 0 −2.5 −2.5 0 Plugging ° C. 1 0 −2 2 point

Example 1

To obtain the gas oil composition of Example 1, desulfurisation was performed using stock oil 1 and commercial desulfurisation catalyst, at liquid-space velocity 1.0 h⁻¹, hydrogen partial pressure 5.6 MPa, hydrogen-oil ratio 150 NL/L, with the unit outlet temperature in the region (temperature) in which polycyclic naphthene dehydrogenation is dominant, until the sulfur content was no greater than 10 ppm by mass. The properties of the resulting gas oil composition are shown in Table 3.

Examples 2 and 3

Gas oil compositions of Examples 2 and 3 were obtained as in Example 1, except that stock oil 2 or 3, respectively, was used instead of stock oil 1. The properties of the resulting gas oil compositions are shown in Table 3.

Comparative Example 1

Gas oil composition of Comparative Example 1 was obtained as in Example 1, except that stock oil 4 was used instead of stock oil 1. The properties of the resulting gas oil composition are shown in Table 3.

TABLE 3 Compar- ative Example Example Example Example Units 1 2 3 1 Monocyclic mass 10.9 11.9 12.0 13.1 naphthenobenzene % content Bicyclic mass 3.9 2.9 4.0 5.3 naphthenobenzene % content Total mass 14.8 14.8 16.0 18.4 naphthenobenzene % content Monocyclic vol 18.2 20.3 19.1 18.8 aromatic content % Bicyclic aromatic vol 2.9 3.0 1.5 1.9 content % Tri- and higher vol 1.0 0.6 0.3 0.4 cyclic aromatic % content Total aromatic vol 22.1 23.9 20.9 21.1 content % Density g/cm³ 0.8357 0.8351 0.8324 0.8359 Sulfur content mass 7 8 3 6 ppm ASTM colour — 0.9 1.1 0.2 0.3 T10 ° C. 226.0 223.0 232.5 225.0 T50 ° C. 290.5 290.5 285.5 289.5 T90 ° C. 345.5 374.0 332.5 334.5 Kinematic mm²/s 4.4 4.2 4.1 4.4 viscosity (at 30° C.) Pour point ° C. −2.5 −5.0 −7.5 −7.5 Plugging point ° C. −1 −2 −6 −2 Cetane index — 57.8 57.7 59.1 57.4 Induction time min 131 155 79 66 

1. A gas oil composition comprising a total aromatic content of at least 20.0% by volume, a bicyclic aromatic content of at least 1.0% by volume, a tri- or higher cyclic aromatic content of at least 0.2% by volume, no more than 18.0% by mass of naphthenobenzenes, and a sulfur content of no more than 10 ppm by mass, and having a density (15° C.) of at least 0.8200 g/cm³, and an ASTM color of at least 0.2, and being obtained by hydrogenation-desulfurization of a stock oil containing a cracked gas oil fraction, the stock oil including a total aromatic content of at least 25.0% by volume, a total naphthene content of at least 15.0% by mass, a bicyclic naphthene content of at least 4.0% by mass, a tricyclic naphthene content of at least 1.0% by mass, and a sulfur content of at least 0.50% by mass, and the stock oil having a 90% distillation temperature of at least 340.0° C.
 2. The gas oil composition according to claim 1, wherein the cracked gas oil fraction is a directly-desulfurized gas oil, and the stock oil contains from 5 to 30% by volume of the directly-desulfurized gas oil, the directly-desulfurized gas oil including a total aromatic content of at least 25.0% by volume, a total naphthene content of at least 15.0% by mass, a bicyclic naphthene content of at least 4.0% by mass, a tricyclic naphthene content of at least 1.0% by mass, and a sulfur content of at least 0.01% by mass, and having a 90% distillation temperature of no higher than 380.0° C., and a density (15° C.) of no higher than 0.8700 g/cm³.
 3. The gas oil composition according to claim 1, wherein the cracked gas oil fraction is a light cycle oil, and the stock oil contains from 1 to 10% by volume of the light cycle oil, the light cycle oil including a total aromatic content of at least 60.0% by volume, a total naphthene content of at least 15.0% by mass, a bicyclic naphthene content of at least 3.0% by mass, a tricyclic naphthene content of at least 1.0% by mass, and a sulfur content of at least 0.07% by mass, and having a 90% distillation temperature of no higher than 370.0° C., and a density (15° C.) of no higher than 0.9800 g/cm³.
 4. A method for producing a gas oil composition comprising a total aromatic content of at least 20.0% by volume, a bicyclic aromatic content of at least 1.0% by volume, a tri- or higher cyclic aromatic content of at least 0.2% by volume, no more than 18.0% by mass of naphthenobenzenes, and a sulfur content of no more than 10 ppm by mass, and having a density (15° C.) of at least 0.8200 g/cm³, and an ASTM color of at least 0.2, comprising hydrogenation-desulfurizing a stock oil containing a cracked gas oil fraction, the stock oil including a total aromatic content of at least 25.0% by volume, a total naphthene content of at least 15.0% by mass, a bicyclic naphthene content of at least 4.0% by mass, a tricyclic naphthene content of at least 1.0% by mass, and a sulfur content of at least 0.50% by mass, and the stock oil having a 90% distillation temperature of at least 340.0° C.
 5. The method for producing the gas oil composition according to claim 4, wherein the cracked gas oil fraction is a directly-desulfurized gas oil, and the stock oil contains from 5 to 30% by volume of the directly-desulfurized gas oil, the directly-desulfurized gas oil including a total aromatic content of at least 25.0% by volume, a total naphthene content of at least 15.0% by mass, a bicyclic naphthene content of at least 4.0% by mass, a tricyclic naphthene content of at least 1.0% by mass, and a sulfur content of at least 0.01% by mass, and having a 90% distillation temperature of no higher than 380.0° C., and a density (15° C.) of no higher than 0.8700 g/cm³.
 6. The method for producing the gas oil composition according to claim 4, wherein the cracked gas oil fraction is a light cycle oil, and the stock oil contains from 1 to 10% by volume of the light cycle oil, the light cycle oil including a total aromatic content of at least 60.0% by volume, a total naphthene content of at least 15.0% by mass, a bicyclic naphthene content of at least 3.0% by mass, a tricyclic naphthene content of at least 1.0% by mass, and a sulfur content of at least 0.07% by mass, and having a 90% distillation temperature of no higher than 370.0° C., and a density (15° C.) of no higher than 0.9800 g/cm³. 